The present invention relates to a printer head mounted on a printer that prints characters and images by the ink-jet printing method.
Ink-jet printers that print characters and images form characters and images with minute drops of ink. The drops of ink are jetted from minute nozzles provided on the printer head. Typical ink jetting methods include the bubble jet(R) method and the piezoelectric method. According to the bubble jet(R) method, ink is heated so as to bubble, and by using the bubbles generated at this time, ink is jetted. According to the piezoelectric method, a piezoelectric plate is deformed, and by the pressure caused in the ink flow path at this time, ink is jetted.
The viscosity of the ink used for ink-jet printers largely changes according to the ink temperature. For example, immediately after the printer is turned on, the ink temperature is low, and the ink viscosity is high. For this reason, in piezoelectric ink-jet printers, the voltage applied to the piezoelectric plate is varied according to the ink temperature. For example, when the ink temperature is low, by applying a high voltage to the piezoelectric plate, the pressure for jetting ink is increased to thereby enable ink of high viscosity to be jetted with reliability, and when the ink temperature is high, by decreasing the pressure, ink of low viscosity is prevented from being jetted in large amount to cause a smear.
However, since it is difficult to measure the temperature of the ink itself, in conventional printers, a thermistor is disposed on the circuit board where a driving circuit for driving the printer head and the like are disposed, the temperature is measured by the change of the resistance of the thermistor, and the pressure applied to the piezoelectric plate is determined according to the change of the temperature. However, in the case of the temperature measurement by the conventional printers, since the distance between the printer head having the nozzles for jetting ink and the piezoelectric plate and the circuit board that performs the temperature measurement is long, it takes time for the change of the printer head temperature to be transmitted to the circuit board, and the ink temperature cannot be accurately measured, so that the optimum pressure cannot be applied to the piezoelectric plate.
Japanese Patent Application Laid-Open No. 2004-82542 proposes a printer head having a plurality of laminated piezoelectric plates, a plurality of individual electrodes disposed on the piezoelectric plates, a common electrode opposed to all the individual electrodes with the piezoelectric plates in between, and sensor electrodes disposed so as to be opposed to the common electrode with the piezoelectric plates in between and to correspond to each individual electrode. The capacitance of the piezoelectric plates between the common electrode and the sensor electrodes is measured, and from the obtained capacitance, the temperature is calculated.